Tetrahydrobiopterin is primarily used in the treatment of metabolic disorders, particularly those related to phenylalanine metabolism. It is essential in managing phenylketonuria (PKU) in patients who are responsive to this cofactor, helping to reduce elevated phenylalanine levels in the blood. Additionally, it plays a critical role in the synthesis of neurotransmitters such as dopamine, serotonin, and norepinephrine, making it valuable in addressing certain neurological conditions. Tetrahydrobiopterin is also utilized in research to study nitric oxide synthase activity and its implications in cardiovascular health. Its ability to support cellular processes makes it a key component in therapeutic strategies for various genetic and biochemical disorders.